Field of the Invention
The invention relates to a control device for a restraint device in a motor vehicle, including a sensor assembly having at least three acceleration sensors with differently oriented sensitivity axes in a plane defined approximately by a longitudinal axis of the vehicle and a transverse axis of the vehicle, and an evaluation device for evaluating acceleration signals furnished by the acceleration sensors.
European Patent 0 419 455 B1 discloses a control device for tripping a restraint device in a motor vehicle, in which a sensor assembly furnishes a longitudinal acceleration signal and a crosswise acceleration signal. An evaluation device of the control device generates a tripping signal for the restraint device in dependence on the longitudinal and crosswise acceleration signals, in order to protect against a front-end impact.
U.S. Pat. No. 4,933,570 discloses a control device for tripping a restraint device in a motor vehicle in which a tripping signal for the restraint device is generated as a function of a signal furnished by an acceleration sensor and a switching signal of a mechanical acceleration switch. Such so-called safing sensors, which are constructed as acceleration switches, serve to prevent the tripping of a restraint device if the acceleration sensor or the evaluation device are defective and furnish a tripping signal. Such an acceleration switch in the ignition circuit typically has a low response threshold and thus furnishes a time slot within which tripping can be carried out on the basis of an evaluation of the signals furnished by the acceleration sensor.
In so-called multichannel control devices for passenger protection, that is control devices which have a plurality of differently oriented acceleration sensors, each individual sensor can be assigned one redundant sensor having the properties of a safing sensor, that is a mechanical acceleration switch, for instance. Accordingly in a control device with two channels, four acceleration sensors or switches would be required to enable the failure of one channel to be ascertained. Such a control device with four acceleration sensors is expensive in terms of componentry and requires a large amount of space, because safing sensors as in the past have very large dimensions.
Published UK Patent Application GB 2 252 414 A discloses a control device for a restraint device in a motor vehicle including a sensor assembly having at least three acceleration sensors with differently oriented sensitivity axes in a plane defined approximately by the longitudinal axis of the vehicle and the transversal axis of the vehicle. An evaluation device evaluates the acceleration signals furnished by the acceleration sensors and outputs a tripping signal to the restraint device as a function thereof. Such a control device is advantageous in particular for controlling a passenger protection system that is equipped with driver, passenger and side air bags as restraint devices, because the direction of an impact can be ascertained on the basis of the measured acceleration signals, and the appropriate restraint device can be selected from the restraint devices which are available, in accordance with the direction.